NONUNIFORM SEDIMENT TRANSPORT - DYNAMICS OF THE ACTIVE LAYER

In the paper the concept of active (or mixing) layer, on which almost all the approaches of non-uniform sediment transport in rivers are based, is reviewed. Accounting fbr bed level fluctuations, mass balance equations are treated in the same way as Reynolds decomposition for turbulent motion: instantaneous variables are decomposed in the average, over a large number of realizations, and in the fluctuating part. The resulting equations are correct from a theoretical point of view and have precise physical meanings. The theoretical findings are compared to some experimental data by Ribberink [1987].